For the purposes of the Acid Rain Program, all emissions limits must be expressed in pounds of SO2 per million British Thermal Unit of heat input (lb/mmBtu).
The factor for converting pounds of sulfur to pounds of SO2 is based on the molecular weights of sulfur (32) and SO2 (64). Limits expressed as percentage of sulfur or parts per million (ppm) depend on the energy content of the fuel and thus may vary, depending on several factors such as fuel heat content and atmospheric conditions. Generic conversions for these limits are based on the assumed average energy contents listed in table A-2. In addition, limits in ppm vary with boiler operation (e.g., load and excess air); generic conversions for these limits assume, conservatively, very low excess air. The remaining factors are based on site-specific heat rates and capacities to develop conversions for Btu per hour. Standard conversion factors for residual oil are 42 gal/bbl and 7.88 lbs/gal.
Table B-1—Conversion Factors
[Emission limits converted to lbs SO2/MMBtu by multiplying as below]
| Unit measurement | Plant fuel type | |||
|---|---|---|---|---|
| Bituminous coal | Subbituminous coal | Lignite coal | Oil | |
| Lbs sulfur/ MMBtu | 2.0 | 2.0 | 2.0 | 2.0 |
| % sulfur in fuel | 1.66 | 2.22 | 2.86 | 1.07 |
| Ppm SO2 | 0.00287 | 0.00384 | 0.00167 | |
| Ppm sulfur in fuel | 0.00334 | |||
| Tons SO2/hour | 2,000,000/(HEATRATE*SUMNDCAP*capacity factor)1 | |||
| Lbs SO2/hour | 1,000/(HEATRATE*SUMNDCAP*capacity factor)1 | |||
1In these cases, if the limit was specified as the “site” limit, the summer net dependable capability for the entire plant is used; otherwise, the summer net dependable capability for the unit is used. For units listed in the NADB, “HEATRATE” shall be that listed in the NADB under that field and “SUMNDCAP” shall be that listed in the NADB under that field. For units not listed in the NADB, “HEATRATE” is the generator net full load heat rate reported on Form EIA-860 and “SUMNDCAP” is the summer net dependable capability of the generator (in MWe) as reported on Form EIA-860.
Table B-2—Assumed Average Energy Contents
| Fuel type | Average heat content |
|---|---|
| Bituminous Coal | 24 MMBtu/ton. |
| Subbituminous Coal | 18 MMBtu/ton. |
| Lignite Coal | 14 MMBtu/ton. |
| Residual Oil | 6.2 MMBtu/bbl. |
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